This invention relates to resonant mechanical systems.
The natural resonant frequency of such a system typically depends on the inertia of the moving element (e.g., a rotating mirror of a resonant beam scanner) and the spring constant of the structure (e.g., a torsion bar) that supports the moving element. The natural frequency may shift for a variety of reasons, including wear and changing environmental conditions, and changes of spring constant or inertia value that occur with angular excursion or as the result of shifts in orientation relative to gravity.
It is known to adjust the natural frequency from time-to-time, after interrupting the motion of the device, by increasing the tension on the support structure, e.g., by tightening a set screw or by increasing or decreasing the inertia value. It is also known to adjust natural frequency by a controllable magnetic spring which supplements or bucks the mechanical spring.
In Shirasaki, U.S. Pat. No. 4,370,019, the resonant frequency of a resonant scanner having a torsion bar suspension is stabilized by controlling the temperature of the scanner.
It has also been proposed to adjust the natural frequency by attaching a bimetallic strip to the resonant system in such a way that the inertia of the mass, and hence the frequency, changes as the temperature of the bimetallic strip changes.